Preheat the oven to 375-degrees. Line a baking sheet with parchment paper.
In a small bowl, use a fork to gently crush a third of the blueberries just slightly so they begin to release their juices. Toss with the rest of the blueberries, lemon juice and zest and cornstarch.
Roll the pie crust out and use the back of the pie press mold to cut the circles out of the dough. You can get 4 circles from the dough, which makes 2 tarts. Repeat with the second pie crust.
Place one piece of the dough into the bottom of the mold and press down gently. Fill the well with 1/4 of the blueberry mixture - take care not to overfill!
Gently top with the second dough circle. Brush the edges with just a little bit of the beaten egg mixture. Squeeze the mold together to seal, then remove and set on the parchment paper. Repeat until you have 4 pie tarts.
Brush the top of each pie with the egg mixture, then bake for 20-24 minutes until the crust is golden and the blueberry mixture is bubbly inside the crust. Remove from the oven and let set for 15-20 minutes before serving.
Top with a sprinkle of confectioner's sugar or serve with ice cream, if desired.